Peng et al. [25] evaluated the performance of a novel solar air collector with pin-fin integrated absorber. Authors developed an original model of collector, which presents some advantages:
1. low cost;
2. high durability;
3. high thermal efficiency, due to high heat transfer coefficient even at lower air mass flow rates and low heat losses;
4. flexibility in applications of fin-pins.
This new model of solar collector contains an absorber with pin fins arrays of different lengths. From recorded data, the heat transfer coefficients of pin-fin arrays and flat plate collector have been obtained for a determined value of the air volume flow rate (19 m3/h). From theoretical model, the formula of the maximum thermal efficiencies ηmax of 25 kinds of pin-fin collectors is given as in Eq. (1) at ambient temperature:
ηmax ¼0:65 s d 0:224 h d 0:149
Aldabbagh et al. [26] discussed about single and double pass solar air heaters (SAH), with wire mesh as packing bed. The schematic views of the single and double pass air collectors are shown in Fig. 3.